Then Kasi Bharadvaja, having heaped up milk-rice in a large bronze serving bowl, offered it to the Blessed One, [saying,] "May Master Gotama eat [this] milk-rice. The master is a plowman, for the Master Gotama plows the plowing that has as its fruit the deathless."

What's been chanted over with versesshouldn't be eaten by me.That's not the nature, brahman,of one who's seen rightly.What's been chanted over with versesAwakened Ones reject. That being their nature, brahman, this is their way of life.Serve with other food & drinka fully-perfected great seer, his fermentations ended, his anxiety stilled,for that is the field for one looking for merit.

The point is that the Buddha doesn't "sing for his supper". Kasi Bharadvaja did not intend to offer food and only offered it after the Buddha chanted that verse. Since the food was not freely given in the first place the Buddha rejected it.